The flybys are all near-equatorial and, moreover, they are so close to the planet that the poles are permanently over the horizon near C/A.

Yet moreover, the interesting thing about the poles, that the bottoms of the craters may contain ice, is by definition something that can't be observed in sunlight, because they're never in sunlight. So far as Mariner 10 showed, there was nothing unusual in the visible areas of the poles.

The interesting thing will be to see the elemental spectroscopy of the north pole where any hydrogen would make a strong signal (as it did on the Moon and Mars). That will have to wait for the orbital mission. The other possibility is that some other element like sulfur is the culprit. I'm betting on ice, though, which would mean that every body in the inner solar system besides Venus has water ice at its poles. Come to think of it, it's probably about a sweep in the outer solar system, too, besides Io.

I was reading an article on Spacedaily, and ran across this real mathematical puzzler:

"Observations during this second Messenger flyby will almost complete the first high-resolution viewing of Mercury, adding another one-third of the planet surface to the 21% of territory not seen by Mariner 10 and first imaged by Messenger in January 2008," says Messenger Project Scientist Ralph McNutt.

I'm scratching my noggin over this one. He appears to be saying: Mariner 10 + Messenger Flyby 1 = 21% unimaged, aka. 79% coverage.But if you add another 33% coverage, you get 112% coverage, which can't be correct.

Or, perhaps: Mariner 10 + Messenger Flyby 1 = 79% Coverage. Of the 21% left unimaged, Flyby 2 will get 1/3 of that missing coverage, aka 7%, so the total coverage will go up to 86%.

Mariner 10 viewed 45% of Mercury. By these numbers, Flyby 1 added 21% and Flyby 2 added 33%, summing to 99%. That works. I think 33% is a bit of an overstatement, but speaking in fractions, 29% could be the real figure, giving a total of 95%.

I still think that's an overstatement, or at least it includes areas on the limb which aren't really being effectively resolved, but the gist is that we'll see more new stuff this time than we did last time. And when it's done, we'll have viewed the great majority of Mercury's surface.

The catch is that it looks totally different depending on phase angle, so we're going to have to see everything at least twice before we've really seen it. But the orbital mission will ace that assignment.

Although flyby #2 largely covers territory already imaged by Mariner 10, I think the resolution should be much better. Also, as JR implies, seeing it at a different phase angle ought to tell us a good bit as well.

It's flyby #3 that may be hard to get excited about. A bit slower, a slightly different phase angle, but otherwise pretty much a repeat of flyby #1. But maybe we'll get lucky and see something cool anyway.

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